This invention relates to an optical memory device comprising a bistable semiconductor laser. The optical memory device is not only useful as an optical memory element but also in an optical master-slave flip-flop device and in an optical signal shifting device or optical shift register. The optical memory elements, the optical master-slave flip-flop device, and the optical signal shifting device are useful in an optical digital computer.
A semiconductor laser having a bistability, is revealed in a letter contributed by H. Kawaguchi to Electronics Letters, Vol. 17, No. 20 (Oct. 1, 1981), pages 741 and 742, under the title of "Bistable Operation of Semiconductor Lasers by Optical Injection." It is possible to manufacture an optical memory device by using the bistable semiconductor laser in the manner which will later be described a little more in detail. The optical memory device is, however, not satisfactorily operable when two optical input signals are simultaneously supplied thereto.
An improved bistable semiconductor laser is disclosed and used in an optical memory device in a report which is read by Y. Odagiri and K. Komtsu at Conference on Lasers and Electro-optics held June 19-22, 1984, and is printed in Technical Digest of the conference, pages 184 through 186, under the title of "Bistable Laser-diode Memory for Optical Time-division Switching Applications" (Report No. THJ3). The Odagiri et al report, however, does not teach selective memory of two optical input signals which are concurrently supplied to the optical memory device.
It is possible by using a pair of optical memory devices, each comprising the improved bistable semiconductor laser, to manufacture an optical master-slave flip-flop device. The flip-flop device must, however, comprise an optical isolator between the optical memory pair as will later be pointed out more in detail. The optical isolator complicates the circuitry and renders it difficult to implement the flip-flop device as an integrated circuit.
To speak of electrical signals, logic operation is carried out at a high speed by a high-speed logic operation device which may comprise Josephson junction devices. Optical signals are often used in representing two-dimensional digital information of a large quantity. Conversion of the optical signals to electrical signals on carrying out logic operation, is objectionable in view of the speed of operation and the power consumption. It is therefore disirable to provide a satisfactorily operable optical memory device in order to carry out the logic operation directly on the optical signals.